This invention generally relates to air recovery electrochemical cells.
Batteries are commonly used electrical energy sources. A battery contains a negative electrode, typically called an anode, and a positive electrode, typically called a cathode. The anode contains an active material that can be oxidized; the cathode contains an active material that can be reduced. The anode active material is capable of reducing the cathode active material. In order to prevent direct reaction of the anode material and the cathode material, the anode and the cathode are electrically isolated from each other by a separator.
When the battery is used as an electrical energy source in a device, electrical contact is made to the anode and the cathode, allowing electrons to flow through the device and permitting the respective oxidation and reduction reactions to occur to provide electrical power. An electrolyte in contact with the anode and the cathode contains ions that flow through the separator between the electrodes to maintain charge balance throughout the battery during discharge.
An air recovery battery, also known as an air assisted or air restored battery, is a battery that uses air to recharge its cathode during periods of low or no discharge. One type of air recovery battery employs zinc powder as the anode, manganese dioxide (MnO2) as the cathode, and an aqueous solution of potassium hydroxide as the electrolyte. At the anode, zinc is oxidized to zincate:
Zn+4OHxe2x88x92xe2x86x92Zn(OH)42xe2x88x92+2exe2x88x92
At the cathode, MnO2 is reduced to manganese oxyhydrate:
MnO2+H2O+exe2x88x92xe2x86x92MnOOH+OHxe2x88x92
When the cell is not in use or when the rate of discharge is sufficiently slow, atmospheric oxygen enters the cell and reacts with the cathode. Manganese oxyhydrate is oxidized to form MnO2:
xc2xdO2+MnOOHxe2x86x92MnO2+OHxe2x88x92
During high rates of discharge, air recovery batteries operate like conventional alkaline cell by reducing xe2x80x9cfreshxe2x80x9d(unreduced) MnO2. During low rates of discharge and periods of rest with no current flow, the xe2x80x9cconsumedxe2x80x9d(reduced) MnO2 is restored or recharged by atmospheric oxygen to the fresh state. Since oxygen must reach the MnO2 for recharging, the cathode of the battery must not be wetted completely by electrolyte. If the cathode is soaked with wet electrolyte, air transport properties inside the cathode degrade and recharging of MnO2 is hampered.
The invention generally relates to air recovery batteries that provide good air distribution to the cathode and protection against leakage of electrolyte.
In one aspect, the invention features a method of assembling an air recovery battery. The method includes (a) inserting a cathode assembly in a can having a wall, the wall having at least one air access opening; (b) placing anode material in the can; (c) inserting a seal assembly into the can, the seal assembly having a current collector; and (d) sealing the can. The air access opening(s) can reduce the diffusion path length for air entering the cell, thereby improving the recharging efficiency of the cell.
In another aspect, the invention features a method of assembling an air recovery battery including (a) placing a bottom cup on an end of a cathode assembly; (b) inserting the cathode assembly and the bottom cup in the can; (c) placing anode material into the can; (d) inserting a seal assembly into the can, the seal assembly having a current collector; and (e) sealing the can. The method can also include placing a barrier layer adjacent to the cathode, forming a groove in the can, and placing an air diffusion layer adjacent to the barrier layer. The bottom cup may allow the cathode to make better electrical contact with the can and generally provides protection against leakage of electrolyte. The groove and air diffusion layer can restrict the cathode assembly from obstructing the air access opening(s).
In another aspect, the invention features an air recovery battery including a can having a wall; at least one air access opening in the wall of the can; anode material disposed in the can; and a cathode assembly in the can.
In another aspect, the invention features an air recovery battery including a can; a cathode assembly in the can; a bottom cup disposed on an end of the cathode assembly; and anode material disposed inside the can. These batteries can include a barrier layer, a groove in the can, and an air diffusion layer. The battery can be a cylindrical battery and/or an air recovery battery.
Other features and advantages of the invention will be apparent from the description of the preferred embodiment thereof, and from the claims.